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Sound auditory theory

Because the human ear hearing system is very complex, so far the human body of its physiological structure and auditory characteristics can not be completely explained from the physiological anatomy point of view. Therefore, the study of human auditory characteristics is currently limited to psychoacoustics and linguistic acoustics.

The auditory range of the human cheap beats by dre ear against different intensity, different frequency sounds is called the sound domain. In the range of the sound domain of the human ear, the subjective feelings of the auditory psychological are mainly loudness, pitch, sound and other characteristics and masking effect, high frequency positioning and other characteristics. Which loudness, pitch, sound can be used to describe the subjectivity with the amplitude, frequency and phase of the three physical quantities of any complex sound, it is also known as the sound "three elements"; and in a variety of sources, the human ear masking effect And other characteristics is more important, it is the basis of psychoacoustics. Let's take a brief look at the above questions.

First, the sound three elements

1. Loudness

Loudness, also known as beats by dre sound intensity or volume, it is that the sound intensity of the strength, mainly depends on the size of the acoustic amplitude. The loudness of the sound is usually measured by the sound pressure (dyne / cm) or the sound intensity (watts per square centimeter). The unit of sound pressure is Pa (Pa), which is called the sound pressure level , In decibels (dB). For the loudness of the psychological feelings, the general use of the unit Song (Sone) to measure, and the definition of lkHz, 40dB pure tone loudness for the song. The relative amount of loudness is called the loudness level, which represents the logarithm of the ratio of the loudness to the reference loudness, in units of the phon, that is, when the human ear feels that a sound is the same as the pure tone of a single frequency of 1 kHz The decibel number of the sound pressure level is its loudness level. Visible, both in the objective and subjective, the concept of these two units is completely different, in addition to 1kHz pure tone, the sound pressure level value is generally not equal to the value of loudness level, the use of attention.

Loudness is the basis of hearing. Normal hearing intensity range of 0dB-140dB (some people think that is -5dB-130dB). Of course, beyond the ears of the audible frequency range (ie, the frequency domain) of the sound, even if the loudness of the larger, the human ear can not hear (that is, loudness is zero). But in the ears of the audible frequency domain, if the sound weak or strong to a certain extent, the human ear is also not heard. When the sound weakened to the human ear just can hear, the sound intensity at this time is called "hearing threshold". General to 1kHz pure tone for the measurement, the human ear can only hear the sound pressure is 0dB (usually greater than 0.3dB that have feelings), sound intensity of 10-16W / cm2 when the loudness level is set to 0 side. And when the sound is enhanced to make people feel pain, this threshold is called "pain threshold". Still to 1kHz pure tone prevailing to make measurements, so that the human ear when the sound pressure level of about 140dB or so.

Experiments show that the threshold and pain threshold with the sound pressure, frequency changes. The area between the auditory threshold and the pain threshold varies with the frequency of the loudness curve (Fletcher-Monson curve) is the hearing range of the human ear. Often that, for 1kHz pure tone, 0dB-20dB for the quiet sound, 30dB - 40dB for the weak sound, 50dB-70dB for the normal sound, 80dB-100dB for the sound, 110dB-130dB for the loud sound. And for audible sounds other than 1 kHz, there are numerous equivalent sound pressure-frequency values ??on the loudness curves of the same level, for example, a 30 dB sound of 200 Hz and a 10 dB sound of 1 kHz sounds the same loudness , This is the so-called "wait ring". Less than 0dB threshold and greater than 140dB pain threshold is not audible, even the most sensitive frequency of the human ear sound, the human ear is also not aware of. The ears of different frequencies of the sound threshold and pain threshold is not the same, the sensitivity is not the same. The pain threshold of the human ear is less affected by the frequency, and the hearing threshold varies considerably with frequency. The ear is most sensitive to the 3kHz-5kHz sound, the sound of a small sound signal can be heard by the human ear, and in the low frequency (such as less than 800Hz) and high frequency (such as greater than 5kHz) the human ear is less sensitive to the sound Much more. Loudness level is small, high and low frequency sound sensitivity is more obvious, and low frequency band than the high frequency sensitivity is more intense, generally should pay special attention to strengthen the low frequency volume. Usually 200Hz - 3kHz voice sound pressure level to 60dB-70dB is appropriate, the frequency range of a wide range of music sound pressure to 80dB-90dB best.

2. pitch

Pitch is also called tone, that the human ear on the tone of the subjective feelings of high and low tone. The objective tone size depends mainly on the level of the fundamental frequency of the acoustic wave, the high frequency is high, and vice versa, the unit is expressed in Hertz (Hz). Subjective feeling of the pitch unit is "beauty", usually defined loudness for the 40 square 1kHz pure tone pitch of 1000 US dollars. Hertz and the "beauty" is the same as the two different concepts of pitch and have contact units.

The feeling of the human ear to the loudness has a range from the threshold to the threshold of pain. The perception of the frequency of the human ear also has a range from the lowest audible frequency of 20 Hz to the highest audible frequency of 20 kHz. The loudness measurement is based on a 1 kHz pure tone, and the pitch measurement is based on a pure tone of 40 dB of sound intensity. Experiments show that the pitch and frequency of the change between the non-linear relationship, in addition to frequency, the pitch is also related to the loudness and waveform of the sound. The change in pitch is proportional to the logarithm of the two relative changes in frequency. Regardless of the original frequency, as long as the two 40dB pure tone frequency increases by one octave (ie 1 times), the human ear feel the pitch changes are the same. In music acoustics, the continuous change in pitch is called the portamento, and one octave is equivalent to the tone raising of an octave. According to the actual feeling of the human ear on the pitch, the human voice frequency range can be relaxed to 80Hz - 12kHz, wide music, the effect is wider.

3. Sound

Sound, also known as sound, by the sound waveform harmonic spectrum and envelope decision. The sound spectrum of the fundamental sound generated by the most clearly known as the pitch, the harmonic of the small vibration generated by the sound said overtone. A single frequency of sound called pure tone, with a harmonic called the polyphony. Each pitch has an inherent frequency and a loudness of different loudness, whereby other sounds with the same loudness and pitch can be distinguished. The ratio of the harmonics of the harmonics of the sound waveform and the decay of the time determines the vocal characteristics of the various sound sources. The envelope is the connection between the crests of each cycle. The steepness of the envelope affects the transient characteristics of the sound intensity. The sound of the sound of colorful, changing, high-fidelity (Hi-Fi) sound goal is to be as accurate as possible transmission, restore the original sound field to restore all the features, so that people actually feel such as sound source positioning, Sense, the thickness of the sense of a variety of on-the-spot sense of the three-dimensional surround sound effect.

In addition, the other physical features that characterize the sound are: the sound value, also known as the length of sound, is determined by the length of the duration of the vibration. The duration is long and the tone is long; From the above three main features of the subjective description of the sound, the ear's auditory characteristics are not completely linear. The sound passes into the human ear after treatment, in addition to the pitch, but also produce a variety of homophonic and their harmony and bad tone, not all of these ingredients can be felt. The human ear has the function of receiving, selecting, analyzing, judging loudness, pitch and sound, for example, the human ear can only feel the envelope of the time domain waveform that has a decisive influence on the sound localization of the high frequency sound signal (especially And the direction of the high-frequency signal is very close to the frequency; These involve complex problems in psychoacoustics and physiological acoustics.

Second, the human ear masking effect

The effect of a weaker sound (masked sound) that is influenced by another strong sound (masking sound) is called the "masking effect" of the human ear. The minimum value of the pure tone that can be heard by the human being in a quiet environment is called the absolute threshold when the masked sound is present alone. Experiments show that the 3kHz-5kHz absolute minimum threshold, that is, the human ear is the most cheap beats by dr dre sensitive to its weak sound; and in the low frequency and high frequency area absolute threshold is much greater. In the range of 800Hz - 1500Hz, the threshold is the most significant frequency change, that is, the language can be the highest in this range. In the case of concealment, to improve the strength of the masked mute, so that the human ear can hear the hearing threshold known as the masking threshold (or masking threshold), the masked mute must be increased the decibel value called masking (or threshold shift ).

1. Masking effect

Experiments have shown that pure tone on pure tone, noise on the pure tone of the masking effect is as follows:

A. pure tone masking

The most effective masking of a pure tone at medium intensity is near its frequency.

low-frequency pure tone can effectively mask the high-frequency pure tone, and in turn the role is very small.

B. noise on the pure tone masking noise is composed of a variety of pure tone, with infinite wide spectrum

If the masking sound is wideband noise, the masked sound is pure tone, then the masking threshold it generates is generally higher than the noise power spectral density of 17 dB in the low frequency band and is relatively flat; If the masking sound is narrowband noise, the masked sound is pure tone, the situation is more complicated. Which is located near the masked sound by the pure tone component composed of narrowband noise that is the critical band of the most obvious masking effect. The so-called critical band means that when a pure tone is masked with continuous noise with a center frequency and with a certain bandwidth, if the pure sound is just able to hear the power equal to the power of the noise in this band, Bandwidth is called the critical band width. The critical band is called Bark, 1Bark = a critical band width. When the frequency is less than 500Hz, 1Bark is about equal to 9 + 41og (freq / 1000), which is about 20% of the frequency of a pure tone. It is generally assumed that there are 24 subcritical bands in the 20 Hz - 16 kHz range. And the masking effect still exists when a pure tone is outside the critical band of the masking sound.

2. Masking type

(1) frequency domain masking

The so-called frequency domain masking means that the masking sound and masked sound at the same time the role of masking effect, also known as masking. At this time, the masking sound has been a function of the masking effect, which is a strong masking effect. Usually, a strong sound in the frequency domain will mask the darkness near the sound at the same time, the weaker the sound from the strong, the more likely to be masked; the other hand, the sound from the strong sound is not easy to be masked. For example, a 1000 Hz tone is 18 dB higher than another 900 Hz pitch, the 900 Hz tone will be masked by 1000 Hz tone. beats earbuds And if the 1000Hz sound than it is far from another 1800Hz pitch 18dB, then the two sounds will be heard at the same time. To hear the 1800Hz sound, the 1000Hz sound is 45dB higher than the 1800Hz pitch. In general, the low frequency sound is easy to mask the high frequency of the sound; in the distance from the strong farther, the absolute threshold than the strong tone caused by the masking threshold is high, then the noise masking threshold should take absolute threshold.

(2) time domain masking

The so-called time domain masking means that the masking effect occurs when the masking sound is different from the masked sound, also known as time masking. Time masking is divided into pre-masking and hysteresis masking. If a masking effect occurs for a period of time before the masking sound occurs, it is called a leading mask; otherwise it is called a hysteresis mask. The main reason for the generation of time domain masking is that the human brain needs to take a certain amount of time to process the information. Time masking also fades with time and is a weak masking effect. Under normal circumstances, the lead masking only 3ms-20ms, and hysteresis mask can last 50ms-100ms.